Conventionally, there has been provided a vehicular glass antenna capable of receiving radio broadcast signals, TV broadcast signals and the like in a vehicle, the vehicular glass antenna being formed by arranging antenna wires on a rear window of the vehicle. Specifically, heater wires of a defogger and the antenna wires formed on peripheral portions of the heater wires are arranged on the rear window of the vehicle. The heater wires and the antenna wires arranged on the rear window serve as a receiving antenna, so that the radio broadcast signals, the TV broadcast signals and the like can be received.
Noise components may be mixed into the radio wave signals of the radio broadcast, the TV broadcast and the like received by the vehicular glass antenna. One of the reasons for the mixing of the noise components into the radio wave signals is the influence of noise contained in the electric power output from a vehicle-mounted battery for heating the heater wires of the defogger. Inversely, the radio wave signals received by the heater wires of the defogger may also be leaked into the vehicle body through an electric supply line.
For this reason, a coil device for antenna for removing noise is connected between the heater wires for preventing the rear window of the vehicle from fog and a DC power supply such as the vehicle-mounted battery. The coil device for antenna uses self-resonant frequency thereof to prevent superimposition of the noise on the radio wave signals received by the vehicular glass antenna and to improve sensitivity for receiving the radio wave signals. Further, in response to the frequency band of the signal wave, high impedance is generated near the resonant frequency to remove the noise superimposed on the radio wave signals.
Ends of the heater wires arranged on the rear window of the vehicle are gathered by a bus bar. Further, impedance is set to a high value between the bus bar and the vehicle body or between the bus bar and the DC power supply, so that the leakage current is restrained. Further, since the radio wave signals received by the antenna need to be prevented from being leaked into the vehicle body through the electric supply line of the defogger, the coil held by a resin member is connected and fixed to the bus bar by means of soldering or the like.
Patent Document 1 discloses a choke coil 10 for reducing noise. A configuration example of the choke coil 10 for the glass antenna will be described below with reference to FIG. 10. In the choke coil 10, a cylindrical Ni—Zn group magnetic core 2 is inserted into a coil 1 formed by winding a copper wire in layers into a tubular shape. Further, both ends of the coil 1 are respectively connected to a metal terminal plate 5 and a metal plate 6 provided on a plastic fixing base constituted by a base portion 3 and a base auxiliary portion 4. A dielectric 7 is inserted between the metal terminal plate 5 and the metal plate 6.
Patent Document 2 discloses a coil device for antenna for removing noise. A configuration example of a coil device for antenna 20 connected to the bus bar will be described below with reference to FIG. 11. In the coil device for antenna 20, a coil portion 12 with a lead wire wound around a magnetic core 11 is mounted on a plastic resin case 13. A terminal board 14 for connecting one end of the lead wire wound around the coil portion 12 thereto is provided on the front side of the case 13. Similarly, a terminal board 15 for connecting the other end of the lead wire wound around the coil portion 12 thereto is provided on the front side of the case 13. The terminal boards 14, 15 face each other in parallel, separated from each other by a prescribed distance in vertical direction.
[Patent Document 1] Japanese Unexamined Patent Application Publication No. H09-213528
[Patent Document 2] Japanese Unexamined Patent Application Publication No. 2005-086402